Health care products maker Covidien PLC Monday said it completed the spinoff of its pharmaceuticals business, Mallinckrodt, into a separate publicly traded company. Covidien, which bases its US headquarters in Mansfield, had disclosed the planned spinoff in December 2011. Covidien executives said the separation allows both firms to pursue their own strategies. Mallinckrodt shares, which began trading on Monday, closed down about 3 percent at $43.92